Title: ------ Circumstellar interaction in supernovae Author: ------- Peter Lundqvist (Stockholm Observatory) ABSTRACT: --------- Here I show two examples where the theory of circumstellar interaction can be important. Limits on circumstellar interaction in Type Ia supernovae can be used to determine the type of progenitor system, and is exemplified by SN 1994D. In core-collapse supernovae, circumstellar interaction is a commen phenomenon, and the most recent subclass normally thought to be strongly affected by circumstellar interaction is narrow-line supernovae, here exemplified by SN 1994W. SN 1994W was unusual in the sense that it showed evidence for only very little nickel-56 in its ejecta. SN 1994D (Lundqvist & Robert Cumming [Stockholm]): -------------------------------------------------- The presence of a circumstellar medium (CSM) in Type Ia supernovae (SNe Ia) is a direct observational way to discriminate between different types of progenitor systems. If embedded in a CSM, interaction of the ejecta with the CSM gives rise to X-ray, radio, UV and optical emission. Using refined modeling we find that X-ray observations in the range 5 - 10 keV, e.g., with AXAF, provide the most useful limits on the mass loss, while high-resolution optical spectroscopy offers the only direct way of identifying circumstellar hydrogen. We apply the models to early observations of SN 1994D, and find an upper limit on the mass loss rate 1.9EE{-5} solar masses per year, assuming a spherically symmetric wind of 10 km s^{-1}. If the supernova would have been observed as early as 3 days after explosion the limit would have been slightly lower 1.4EE{-5} solar masses per year. Major uncertainties of the analysis are the geometry of the CSM and the outer structure of the progenitor, which both affect the X-ray radiation from the supernova. SN 1994W (Lundqvist, Jesper Sollerman [Stockholm] & Cumming): ------------------------------------------------------------- Spectroscopic and photometric observations of the luminous narrow-line Type IIP (plateau) supernova 1994W show evidence for circumstellar excitation and a low mass of ejected nickel-56. After the plateau phase (t > 120 days), the light curve dropped by roughly 3.5 mag in V in only 12 days. Between 125 and 197 days after explosion the supernova faded substantially faster than the decay rate of cobalt-56, and by day 197 it was 3.6 magnitudes less luminous in R compared to SN 1987A. The low R-luminosity could indicate < 0.0026{+0.0017}{-0.0011} solar masses of nickel-56 ejected at the explosion, but the emission between 125 and 197 days must then have been dominated by an additional power source, presumably circumstellar interaction. Alternatively, the late light curve was dominated by cobalt decay. In this case, the mass of the ejected nickale-56 was 0.015{+0.012}{-0.008} solar masses, and the rapid fading between 125 and 197 days was most likely due to dust formation. Though this value of the mass is higher than in the case with the additional power source, it is still lower than estimated for any previous Type II supernova. The implications of the type of progenitor is discussed. The supernova's narrow (of order 1000 km s^{-1}) emission lines were excited by the hot supernova spectrum, rather than a circumstellar shock. The thin shell from which the lines originated was most likely accelerated by the radiation from the supernova. (Figures for SN 1994W available on request only.) To appear in: ------------- Santa Barbara ITP Workshop on ``Supernova Explosions: Their Causes and Consequences'' (Proceedings will only be available on the web, i.e., there will be no paper proceedings. Please, check: http://www.itp.ucsb.edu/snovaesched.html).